Video compression refers to reducing the quantity of data used to represent digital video images, and uses a combination of spatial image compression and temporal motion compensation. Video compression may also be viewed as a conceptual example of source coding in information theory. Several methods are known for video compression such as H.264/MPEG-4 Part 10 or AVC (Advanced Video Coding). H.264 is a block-oriented motion-compensation-based codec standard developed by the ITU-T Video Coding Experts Group (VCEG) together with the ISO/IEC Moving Picture Experts Group (MPEG).
Digital watermarking is the process of embedding information into a digital signal in a way that is difficult to remove. The digital signal may represent, for example, audio, picture, video or other information. If the digital signal is copied, then the watermark information is also carried in the copy. A signal may carry several different watermarks at the same time.
In visible watermarking, the information is visible in the picture or video. Typically, the information is text or a logo which identifies the owner of the media. One common example of using a visible watermark is when a television broadcaster adds its logo to the corner of transmitted video program material.
In invisible watermarking, however, information is added as digital data to audio, picture or video data, but the watermark is not visibly or audibly perceived as such, although it may be possible to detect that some amount of information is hidden. The watermark may be intended for widespread use and is thus be easy to retrieve or it may be a form of steganography, where a party communicates a secret message embedded in the digital signal. In either case, as in visible watermarking, the objective is to attach ownership or other descriptive information to the signal in a way that is difficult to remove. It is also possible to use hidden embedded information as a means of covert communication between individuals.
One application of watermarking is in copyright protection systems, which are intended to prevent or deter unauthorized copying of digital media. In this use, a copy device retrieves the watermark from the signal before making a copy, and the device makes a decision to copy or not depending on the contents of the watermark. Another application is in source tracing. A watermark is embedded into a digital signal at each point of distribution. If a copy of the work is found later, then the watermark can be retrieved from the copy and the source of the distribution is known. This technique has been reportedly used to detect the source of illegally copied movies. Annotation of digital photographs with descriptive information is another application of invisible watermarking
Previously, robust watermarking for H.264 video is based on using an uncompressed domain technique, or using a joint encoded technique. With respect to the uncompressed domain technique, the video is uncompressed first, and then it is watermarked with an uncompressed domain watermarking technique. For joint encoding, a watermark is embedded during the H.264 encoding process. This is also more difficult due to the fact that one single change in the bit stream may introduce an unwanted error that propagates to future blocks or future frames.